This invention relates to a method and apparatus for the control of a combustion engine. While the general principles and teachings hereinafter disclosed are applicable to all combustion engines, the invention is hereinafter described in detail in connection with its application to a reciprocating, fuel-injected, spark-ignition internal combustion engine.
As used herein, the term "engine" refers to a device which converts heat energy, released by combustion of a fuel, into mechanical energy in a rotating output shaft of the engine. Also, the term "combustion" is defined as the rapid chemical union of a fuel with oxygen, accompanied by the liberation of useful heat energy. Also, as used herein, the term "binary number" means a number represented by a plurality of bits of information having either of two states.
In an engine, the energy conversion process takes place in a combustion chamber. Various means may be provided for controlling the characteristics of this energy conversion process. For example, means may be provided for controlling the amount of fuel metered into the combustion chamber, for controlling the amount of air supplied to the combustion chamber, for controlling the ratio of fuel to air, and, in a spark-ignition engine, for controlling the timing of sparks supplied to the engine. Also, a recent development used in connection with spark-ignition internal combustion engines for the purpose of effecting a reduction in undesirable exhaust emissions is exhaust gas recirculation (EGR). Where EGR is employed, it is very desirable to provide means for controlling the amount of exhaust gas recirculated to the engine combustion chamber.
A common feature of all engine control systems is that they employ means for sensing at least one condition of the engine while it is operative in effecting the energy conversion process. As a result of sensing this condition, one or more of the means for controlling the energy conversion process are adjusted to the extent required to obtain a desired result.
To illustrate what is meant by the phrase "means for controlling the energy conversion process of an engine", these being controlled variables, consideration may be given to a throttled, spark-ignition, fuel-injected internal combustion engine. In such case, the controlled variables are throttle angle, which controls the amounts of air supplied to the engine, fuel flow per cycle, fuel-injection timing, ignition timing, and, if EGR is used, the settings of the means used to control the amount of exhaust gases recirculated through the engine. To effect control of these variables that determine the characteristics of the energy conversion process, various engine conditions may be sensed while the engine is operative. Thus one or more of the following variable engine conditions may be sensed: crankshaft position, engine speed, mass air-flow into the engine, intake-manifold pressure, throttle angle, EGR-valve position, throttle-angle rate of change, engine-speed rate of change, fuel temperature, fuel pressure, EGR-valve rate of change, vehicle speed and acceleration, engine coolant temperature, engine torque, air-to-fuel ratio, exhaust emissions, etc. Other sensed conditions may include ambient temperature, ambient air pressure, humidity, transmission gear position, and perhaps others.